Computers typically have numerous types of cabling used to connect various sub-assemblies within such computer. When computer busses (or other type of interfaces containing plural electrical signals) are connected from one sub-assembly to another via cabling, it is possible that termination circuits are required to improve the quality of electrical signals traveling through the cabling. These termination circuits modify the effective impedance `seen` by the electrical signals, and reduce reflections which might otherwise occur in a non-terminated cable.
Circuits used to terminate a cable connecting a disk controller with a disk drive typically consist of a resistor-pack, or RPAK, containing a plurality of resistors in a discrete package. The given resistor in the RPAK would be connected to a given conductor in the cable. Each resistor in the RPAK typically has a resistance value substantially equal to the resistance value of a single conductor within an interconnecting cable. These RPAKs are manually inserted and removed from a disk drive electronic card, depending on where the particular disk drive is with respect to the interconnecting cable and other disk drives that may be attached to such cable. For example, a given cable may be daisy-chained, where a plurality of connectors are dispersed at various intervening locations across the length of a cable. For the disk drive located at the end of an interconnecting cable, an RPAK would be inserted to properly terminate the cable. For disk drives plugged into intermediate locations within a `daisy-chained` cable connection, the RPAKs are removed.
An example of the above described cable interconnection scheme is a small computer system interface, or SCSI, bus. This is a common bus used for interconnecting a plurality of disk drives to a disk controller. Another popular disk drive interconnection bus is known as IDE. Both of these busses use termination circuits to terminate interconnecting cables.
Originally, the number of data bits in these SCSI and IDE busses was eight (8) bits. With the higher performance computer systems in existence today, the need to expand these data paths to sixteen (16) bits or greater has evolved. However, this evolution has caused problems in maintaining compatibility between newer sixteen bit wide bus interfaces and the older eight bit wide bus interfaces.
There is a growing movement to ease operator set-up when installing or removing devices in a computer, particularly in the world of personal computers. Various types standards are being defined to ease the burden on the end user when modifying the configuration of his/her computer. One such standard is known as Plug-n-Play, whose primary objective is to reduce the number of hardware/software changes that are required to a particular computer system when modifying its internal structure or make-up.
Plug-n-Play systems currently allow for the auto-termination of eight bit busses. For such a system, there are two connectors and one terminator RPAK (with eighteen resistors), as there are eighteen conductors that need to be terminated in an eight bit SCSI bus (eight data lines and ten control/status lines). However, with the advent of sixteen bit busses, a problem exists on how to provide for auto-termination of systems having a combination of dissimilar bus widths.
Some systems provide auto-termination at the peripheral side of the SCSI bus, such as that described by Lewis et al in U.S. Pat. No. 5,313,595, which is hereby incorporated by reference. However, this type of system does not address auto-termination on the host side of the SCSI bus, or how to deal with complexities relating to a plurality of dissimilar types of SCSI devices having dissimilar data widths.
It is an object of the present invention to provide an improved interconnection system.
It is a further object of the present invention to provide an interconnection system for Plug-n-Play types of systems.
It is yet another object of the present invention to provide a method and system for automatically determining the types of devices on an interconnecting bus, and providing proper termination of interconnections for such bus.
It is still another object of the present invention to provide a method and system for automatically terminating interconnecting cables in a system having a plurality of dissimilar bus widths.